Atlantoaxial Instability

For today's Medical Monday, I am featuring a condition that affects up to 30% of people with Down syndrome. It is called Atlantoaxial Instability (or AAI for short) and can cause serious problems if it is undetected.

The Vertebral
Column

The spine is made up of large bones called vertebrae which surround the spinal cord.  These are divided into groups or sections for the purpose of descriptive location:  there are 7 cervical (red), 12 thoracic (blue), 5 lumbar (yellow) and the pelvic (green).  The first vertebrae (C1) is referred to as "atlas" and the second (or C2) is referred to as the "axis". Muscles and strong ligaments allow movement, including flexion (forward tilt of the head) and extension (backward tilt of the head).

Most people with Down Syndrome have hypotonia or low muscle tone and often have hypermobile joints (due to lax ligaments).  When this occurs, C1 and C2 can become misaligned;  this is referred to as Atlantoaxial Instability.

Many people (10-20% of people with DS) have what is known as 'asymptomatic' AAI (as in not causing them any symptoms).  This is found on an x-ray which should be routinely performed around the age of 3.  However, 1-5% have 'symptomatic' AAI, which causes a variety of problems.

When the atlas and the axis are misaligned (also known as subluxation), the spinal cord inside can become compressed which can cause serious symptoms and even death.  Among those symptoms are:

Plate from Grey's Anatomy, showing the occipital portion
of the skull, the Atlas (C1) and Axis (C2).

• Lack of Coordination 
• Clumsiness 
• Difficulty walking
• Walking abnormally
• Tiring easily
• Limited neck movement and/or nerve pain
• Tightness in the muscles
• Muscle contractions or spasms

If any of these symptoms are experienced by a person with Down syndrome, they would require a full work up by a Neurologist, which might include X-rays, MRI and CT scans.  Surgical stabilization of the joint may be necessary, however depending on the severity of the AAI, other treatments such as traction, collars and muscle relaxants may be prescribed. 

Those with asymptomatic AAI would require no treatment, however sports would be limited to no-contact and low impact and a brace might have to be worn for protection.

Those without either condition are still recommended to have a neck (or 'cervical') x-ray series done and wear neck protection if playing contact sports.